[TowerTalk] Rooftop vertical grounding

[Guy Olinger, K2AV]

The best place to take your ground wire from the roof structure is right
down to the ground rod at the power service entrance and tie it in. You
will be well served to take the feedline the same way if that is
possible. If not, run a second ground wire along the feedline path and
add a ground rod at or directly below the feedline entry point. At the
point where the feedline veers away, bond the coax shield to the ground
wire. This is where to put lightning arrestor devices.

In this second configuration you will need to run an underground bare #4
wire from the feedline groundrod to the power service entrance ground,
using the shortest possible path. This is required to keep a grounded
item close to one ground rod from being at an elevated potential with
respect to the other ground during the rise time of a nearby lightning
strike. Minus this tie, the lightning spike will use miscellaneous wire
and equipment in your house to complete the circuit.

Note that having the second ground on the far side of the house with a
basement in between is a real problem. Pick the feedpoint entry to
eliminate the need for an impossible ground tie between the two
grounding points.

- - . . .   . . . - -     .   . . .     - - .   . - . .

73, Guy
k2av@contesting.com
Apex, NC, USA

----- Original Message -----
From: berferd <jrp@dimensional.com>
To: <towertalk@contesting.com>
Sent: Thursday, February 10, 2000 4:35 PM
Subject: [TowerTalk] Rooftop vertical grounding


>
> Hello everyone.
>
> My name is Jeff and I'm a new ham.  I received my general class
> license approximately two weeks ago.  Call sign is KC0HEP.  I
> live in Colorado.  I'm not putting up a tower (yet), so if this
> not the appropriate forum for my questions, please chastise
> me and I'll be on my way.
>
> My first antenna is going to be a vertical.  The Butternut HF9V
> to be exact.  I'm planning on mounting it the roof of my house
> with the counterpoise kit on a tripod.  The antenna is about
> 26 feet in height.
>
> I'm trying to figure out the best way to ground this thing in
> case Mother Nature decides to zap it.
>
> The antenna needs to be mounted in the middle of the roof because
> there will be four rope guys going to the corners of the roof.
> So the down conductor(s) will have to take a turn when it gets
> to the edge of roof.  I understand from reading messages in
> the towertalk archive that the turn should be as small as
> possible.  Does anyone know how tight I can go?  If I did get
> a lightning strike and the bolt reaches the turn, I don't
> know where it else it could go (other than down the coaxial
> cable).  All the fences around here are wood and there aren't
> any above ground utilities.  So wouldn't it continue down
> the conductor to ground in spite of the turn?
>
> I'm thinking about two down conductors of #1/0 gauge going down
> adjacent corners of the house into separate ground rods tied
> together.  Is this enough?  Can I get away with only one down
> conductor?  It is my understanding that the down conductor
> surface area should be at least equal to or larger than the
> total surface of the coax.  I'd like to use insulated conductors
> if possible.  Any reason why I should use bare conductors?
>
> Since my shack will be in the basement, I'm looking at
> installing an entrance panel at the top of the wall of the
> shack (have to see how much room I have between the top of
> the foundation and the floor above to see if I can squeeze
> one in there).  So the outside of the entrance panel would
> be tied into earth ground and the inside would be tied
> into the equipment bus bar.  I have a electrician coming
> over to see about moving my service ground (which currently
> resides under a concrete patio) somewhere else so I can
> tie into it.
>
> The part that scares the hell out of me is tying my shack
> bus bar into the antenna ground.
>
> Let's say I've done everything by the book with respect
> to lightning protection.  What if the energy from the
> strike isn't dissipated by ground quickly enough?  What's
> to stop the energy from finding it's way to my equipment?
> I'd like to have a good RF ground for sure, but I'm worried
> about protecting my equipment.  I'd like to set something
> up where I could not only disconnect the antenna feed
> from the shack, but also disconnect the bus bar from
> ground when not operating.  I'm thinking that this way,
> if a lightning strike does occur (when I'm not operating)
> the equipment is isolated.  Of course *all* connections
> would be severed (power, etc.)
>
> Is this a good idea?  Comments?  Flames?
>
> Thanks for reading this far.
>
>
> Jeff
> KC0HEP
>
>
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>


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